Intrinsically conductive polymers including polyaniline, polypyrrole, polythiophene and derivatives thereof exhibit variable electrical conductivity as a result of being doped by a doping process, unlike conventional electrical insulating polymers. Hence, many attempts have been made to apply such conductive polymers to fields including antistatic materials, film materials for capacitors, electrochromic devices or displays, and so on.
However, conductive polymers are insoluble in a solvent attributable to strong intermolecular attractions and effects of dopant anions, undesirably resulting in poor processability. Even in the case of poly(3,4-ethylenedioxythiophene)/polystyrene acid (Clevios P, purchased from H. C. Starck GmbH, Germany) which overcomes the above problem and is currently commercially available, it is provided in the form of being dispersed only in water, and thus the application thereof is limited to specific fields.
In order to solve such problems, different methods have been devised.
For example, U.S. Patent Application No. 2003/0088032 A1 discloses a method of preparing a conductive polymer which is dispersible in an organic solvent such as nitromethane, propylenecarbonate or the like by copolymerizing a heteroaromatic conductive polymer block with an ethyleneoxide block for imparting solubility in an organic solvent or by end-capping a conductive polymer oligomer with a methacrylate or another acrylate group.
This method, which changes a bond system itself of the conductive polymer chain to impart dispersibility in an organic solvent, is problematic in that synthesis and polymerization procedures are multi-staged thus making it difficult to prepare the conductive polymer and to control the properties thereof, and also that the synthesized conductive polymer has poor electrical conductivity.
Furthermore, there was reported a method of synthesizing a conductive polymer compound in which a stereostructure stabilizer such as polyvinylalcohol, polyvinylacetate or cellulose derivative is used so that the resultant polymer compound particles have a small size thus facilitating the dispersion of the polymer compound in the solution (Polymer, vol. 33, pp. 4857, 1992). However, this method suffers because polyvinylalcohol is used only as the dispersion stabilizer and does not function as a dopant, and thus acts as an impurity when a final electrical conductive film is formed, undesirably reducing electrical conductivity.